The coefficient of thermal expansion (CTE) of a polymer material—specifically, a cured epoxy resin compound—is about 50 to 80 ppm/° C., significantly high, on the level of several to tens of times the CTE of a inorganic material such as a ceramic material or a metal, (for example, the CTE of silicon is 3 to 5 ppm/° C., and the CTE of copper is 17 ppm/° C.). Thus, when the polymer material is used along with the inorganic material or the metal in a semiconductor, a display, or the like, the properties and processability of the polymer material are remarkably limited due to the different CTEs of the polymer material and the inorganic material or the metal. In addition, during semiconductor packaging in which a silicon wafer and a polymer substrate are used side by side, or during a coating process in which a polymer film is coated with an inorganic shielding layer to impart gas barrier properties, product defects such as the crack formations in an inorganic layer, the warpage of a substrate, the peeling-off of a coating layer, the failure of a substrate, and the like, may be generated due to a large CTE-mismatch between constituent materials during processing and/or due to changes in service temperatures.
Because of the high CTE of the polymer material and the resultant dimensional change of the polymer material, the development of technologies such as next generation semiconductor substrates, printed circuit boards (PCBs), packaging, organic thin film transistors (OTFTs), and flexible display substrates may be limited. Particularly, at the current time, the industries of the semiconductor and PCB fields are facing challenges in the design of next generation parts requiring high degrees of integration, miniaturization, flexibility, performance, and the like, in securing processability and reliability in parts due to polymer materials having significantly high CTE compared to metal/ceramic materials. In other words, due to the high thermal expansion properties of the polymer material at processing temperatures, when the parts are manufactured, defects may be generated, processability may be limited, and the design of the parts and securing of processability and reliability therein may be objects of concern. Accordingly, improved thermal expansion properties or the dimensional stability of the polymer material are necessary in order to secure processability and reliability of electronic parts.
In general, in order to improve thermal expansion properties—i.e., to obtain a low CTE in a polymer material such as an epoxy compound, (1) a method of producing a composite of the epoxy compound with inorganic particles (an inorganic filler) and/or fibers and (2) a method of designing a novel epoxy compound having a decreased CTE have been used.
When the composite of the epoxy compound and the inorganic particles as the filler is formed in order to improve thermal expansion properties, a large amount of silica filler particles, having a size in the range of several tens of nm to several tens of μm is required to be used to obtain a CTE decrease effect. However, due to the presence of the large amount of inorganic particles, the processability and physical properties of the parts may be deteriorated. That is, the presence of the large amount of inorganic particles may decrease fluidity, and voids may be generated during the filling of narrow spaces. In addition, the viscosity of the material may increase exponentially due to the addition of the inorganic particles. Further, the size of the inorganic particles tends to decrease due to semiconductor structure miniaturization. When a filler having a particle size of 1 μm or less is used, the decrease in fluidity (viscosity decrease) may be worsened. When inorganic particles having a large average particle diameter are used, the frequency of insufficient filling in the case of a composition including a resin and the inorganic particles may increase. While the CTE may largely decrease when a composition including an organic resin and a fiber as the filler is used, the CTE may still be high as compared to that of a silicon chip or the like.
As described above, the manufacturing of highly integrated and high performance electronic parts for next generation semiconductor substrates, PCBs, and the like may be limited due to the limitations in the composite technology of epoxy compounds. Thus, the development of a polymer composite having improved heat resistance properties—namely, a low CTE and a high glass transition temperature—is required to overcome the challenge of a lack of heat resistance properties due to a high CTE and processability of a common thermosetting polymer composite.